The streets can be a fierce world for buskers who are exposed to the mercy of city police. However, musicians in San Francisco can perform at train stations for free as long as they stay outside the paid zones such as the platforms and trains.
You don’t need to pay any rent to use this acoustic environment, but you do need to apply for a “Permit to Engage in Expressive Activity” as “BART requires those who wish to exercise their right to free speech to have a permit while on BART property.” (BART = Bay Area Rapid Transit)
Leo was playing his cello when I met him at the 16th Street and Mission station. He explained that competition for a spot at the train stations can be intense, especially during rush hour when the audience reaches its peak, so “you have to get here pretty early to get a spot.”
More information about the permit: http://www.bart.gov/about/business